2. Today’s Web Seminar
How to Calibrate an IR Thermometer
May 7, 2013
How do you know that your infrared calibrations are accurate? Register for this free
webinar from Fluke Calibration to learn how to improve the accuracy of your infrared
thermometer calibrations. Topics discussed will include sources of uncertainty,
calibration equipment required, overview of the calibration procedure, review of a
sample uncertainty budget, and recommendations for reporting results.
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3. Your Presenter
Frank Liebmann
• B.S. Electrical Engineering University of Utah
• 9 years with Fluke/Hart Scientific
– Sr. Design Engineer
– Radiation Thermometry Engineer
• Chairman ASTM Subcommittee E20.02 on Radiation Thermometry
• 20 years U.S. Army
• frank.liebmann@fluke.com
• Phone: 801.763.1700 3
4. What we will be talking about…
• Sources of uncertainty
• Calibration equipment
• Traceability schemes
• Laboratory setup
• Calibration procedure
• Uncertainty analysis
• Reporting your results
• Questions
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5. Introduction
• IR thermometry calibration can be accurate
• Proper procedure must be followed
• ASTM E2847, “Standard Practice for Calibration and
Accuracy Verification of Wideband Infrared
Thermometers”
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6. Sources of Uncertainty
• Major
– Emissivity estimation of the calibration source
– Field-of-view of the infrared thermometer
– Temperature gradients on the radiation source
– Improper alignment of the infrared thermometer
– Calibration temperature of the radiation source
– Ambient temperature
– Reflected temperature
• Minor
– Source heat exchange
– Atmospheric absorption
– Noise
– Display Resolution
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7. Calibration Equipment
• Mandatory
– Thermal radiation source
– Transfer Standard
– Ambient Temperature Thermometer
– Mounting Device
– Distance Measuring Device
• Non-mandatory
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9. Thermal Radiation Source
Size of the thermal radiation source
• For Fluke IR thermometer models
– 5” (~ 125 mm) diameter is enough
• Other IR thermometer manufacturers
– Consult manufacturer
– Testing
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10. Transfer Standard
• Contact Thermometry (Scheme I)
– PRT, thermistor, or thermocouple
• Non-contact Thermometry (Scheme II)
– Radiation thermometer
• More discussion under ‘Traceability Schemes’
• Implementation
– Internal
– Third-party laboratory
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11. Ambient Temperature Thermometer
• Monitor laboratory conditions
• Use to control uncertainties
– Reflected ambient radiation
– Ambient temperature
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12. Mounting Device
• Holds IR thermometer
• Maintains alignment and measuring distance
• May be any of the following
– A tripod
– A fixture
– A hand
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13. Distance Measuring Device
• Used to verify measuring distance
• Measuring distance: “Distance or distance range between
the radiation thermometer and the target (measured
object) for which the radiation thermometer is designed.”
IEC 62492-1
• Use:
– Tape measure
– Measuring rod
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17. Laboratory Setup
• Laboratory temperature limits
– Ambient temperature uncertainty
– Reflected temperature uncertainty
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18. Laboratory Setup - Incorrect
• A heat source facing a
flat-plate
• A flat-plate facing an
exterior wall
– Especially a window
• A flat-plate in the
vicinity of air drafts
– HVAC vent
– Commonly used traffic
way
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19. Laboratory Setup - Incorrect
• A heat source facing a
flat-plate
• A flat-plate facing an
exterior wall
– Especially a window
• A flat-plate in the
vicinity of air drafts
– HVAC vent
– Commonly used traffic
way
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20. Laboratory Setup - Incorrect
• A heat source facing a
flat-plate
• A flat-plate facing an
exterior wall
– Especially a window
• A flat-plate in the
vicinity of air drafts
– HVAC vent
– Commonly used traffic
way
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21. Laboratory Setup - Correct
• Well controlled reflected temperature
• Sufficient spacing from other instruments
• Isolated from air drafts in room
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24. Preparation
• Allow infrared thermometer time to reach room
temperature (at least 15 minutes)
• Lens cleaning
– Only clean if requested by customer
– Clean per manufacture's instructions
• Set up any special equipment
• Set radiation source to desired temperature
• Allow radiation source time to stabilize
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25. Calibration Points
What calibrations point to use?
• Determined by the customer
• Laboratory may offer advice
– Over wide range, minimum 3 points
– Narrow range, 1 or 2 points may be fine
• Best practice to perform calibration from lowest
cal point to highest
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26. Calibration Procedure
Procedure for each calibration point
• Set IR thermometer reflected temperature (if available)
• εIRT = εS
– εS is adjustable on a 4180 and 4181
• Align IR thermometer
– Set distance (Z-direction)
– Align side-to-side and up-and-down (X- and Y-directions)
– IR thermometer should be no more than 5° from normal to target
surface
• Make measurement
– Make measurement 10 times IR thermometer response time
– For instance: IR thermometer respose time 0.5 s, make measurement for 5 s
• Procedure < 15 s
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29. Uncertainty Analysis
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Uncertainty Desig. Type
U(100 °C)
(°C)
Source Calibration temperature U1 B 0.268
Source emissivity U2 B 0.128
Reflected ambient radiation U3 A 0.031
Source heat exchange U4 B 0.012
Ambient Conditions U5 B 0.001
Source uniformity U6 A 0.163
Infrared
Thermometer
Size-of-source effect U7 B 0.019
Ambient temperature U8 A 0.050
Atmospheric absorption U9 B 0.020
Noise U10 A 0.100
Display Resolution U11 A 0.058
Combined Expanded Uncertainty (k=2) 0.364
30. Reporting Your Results
Every report of calibration should contain:
• Title
• Unique identification of the calibrated infrared thermometer
• Record of the person who performed the calibration
• Date of calibration
• Source temperature versus infrared thermometer readout
temperature
• Measuring distance
• Emissivity setting of the infrared thermometer
• Diameter of the source
• Ambient temperature
• Description of the aperture including aperture distance (if used)
• Measurement uncertainties
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31. Supplemental Information
• Description of the calibration procedure
• List of reference instruments
• Traceability statement
• Description of the uncertainty budget
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